1. Field of the Invention
The present disclosure relates to a measuring device and system that allows convenient and simultaneous measurement of flow and conductivity of permeate produced by reverse osmosis elements while they are installed in a pressure vessel and operated in an RO train.
2. Description of the Related Art
Spiral wound reverse osmosis membrane elements are widely used for the desalination of water in plants of increasingly higher capacity. A commercial membrane element measures 1000 mm (40 inches) in length and 200 mm (8 inches) in diameter and weighs about 16 kg (40 lbs). A single element produces a permeate flow of 12 m3/d-24 m3/day (3200-6400 gallons per day). A single desalination plant producing 200,000 m3/day (50 million gallons of water per day) of permeate may require as many as 15,000 such spiral wound elements to produce the designed permeate capacity. The individual elements are loaded into fiberglass pressure vessels arranged in racks to form a single RO train. In large RO systems one train may consist of 100-200 pressure vessels. Several trains may operate independently in any single desalination plant. Six to eight elements are loaded into a single pressure vessel. Accordingly, 600 to 1600 elements may operate in a single train. Once loaded in the pressure vessels, membrane elements are only removed at the time of element replacement (usually every 3-10 years of operation) or when required for special testing. Removal of membrane elements from pressure vessels requires the complete shut down of RO train operation.
The performance of individual elements is usually known prior to installation in the RO system. After installation, the performance of elements may change due to membrane fouling. The effect of membrane performance deterioration is observed by measuring the permeate flow, permeate conductivity and pressure drop of a complete RO train. In some cases, the permeate conductivity of individual pressure vessels can be measured. Measurement of permeate flow and permeate conductivity of individual elements is not practical with current technology in a commercial RO unit. Usually, the effect of fouling on element performance is not uniform through the system. After performance of an RO system has deteriorated to a certain level, a performance improvement can be achieved by membrane cleaning or partial or complete replacement with new elements. The major obstacle to efficient element replacement is the absence of a convenient method for measuring the performance of individual elements while they are installed and operating in an RO train.